Recently, a confocal microscope is a device used to irradiate given wavelength of light to a sample, to pass the reflected light to a confocal aperture like a pinhole, and to detect only the light emitted from the focus of an objective lens through a photo detector.
FIG. 1 is a concept view showing a confocal optical system to which the principle of a general confocal microscope is applied.
Referring to FIG. 1, the confocal microscope includes: a light source 11 for irradiating laser light; a beam splitter 13 for converting the advancing path of the incident light thereinto; an objective lens 15 for focusing the light irradiated from the light source 11 thereto; and a photo detector 19. Further, the confocal microscope includes an aperture 17 disposed between the beam splitter 13 and the photo detector 19 so as to allow only image being in focus to be sent toward the photo detector 19.
The light source 11 irradiates the laser light having the wavelength band adequate to a fluorescent material labeled on the sample so as to induce the emission of the fluorescent material, and the emitted fluorescent signals are focused by the objective lens 15. Next, the focused fluorescent signals are focused to the photo detector 19 via the beam splitter 13. At this time, the image being not in focus is blocked by the aperture 17, and therefore, the fluorescent signal image being in focus is detected through the photo detector 19.
The light reflected from the outside of the focal plane of the objective lens 15 is not passed through the aperture 17 and thus not detected through the photo detector 19, so that the confocal microscope has a high resolution limit in the direction of an optical axis thereof and further has a higher resolution limit in a vertical direction with respect to the optical axis than the existing optical microscope.
Further, the image can be obtained through optical sectioning using the laser light source, without mechanical cutting of the sample, so that the confocal microscope can observe a given plane of the sample, obtain the three-dimensional image of the sample, perform various image processing, observe the variations of ions and pH for live materials, and analyze the correlation between the materials within cells using the properties of the fluorescent material.
Such confocal optical system having high resolution limit and three-dimensional image acquiring performance has been recently adopted in a variety of professional fields such as cell biology, semiconductor chip inspection, and large optical lens or mirror used for artificial satellite of aerospace industry, and further, the confocal optical system has been widely applied to inspect the quality of semiconductor display parts, automobile parts, portable camera and copier parts over a variety of fields closely related to living.
According to the above-mentioned confocal microscope, on the other hand, the laser light irradiated from the light source 11 is focused to form the image on the surface of the sample through the microlens as the objective lens 15 located on the lower portion of the confocal microscope, and as shown in FIG. 2, the light L is incident into the microlens 15 in a form of parallel light, focused through the spherical shape of the microlens 15, and irradiated to the surface of the sample.
According to the confocal optical system, however, the focal length of the light incident to the form of parallel light and focused through the microlens 15, that is, the focal length f of the microlens 15 is very short, so that the working distance W from the surface of the sample to the microlens 15 is not sufficiently ensured upon the measurement of the sample, thus undesirably making the optical system and the surface of the sample brought into contact with each other. Specifically, as shown in FIG. 3, if the surface S of the sample 20 is irregular and bent, the microlens 15 located on the lower portion of the optical system and the surface S of the sample 20 are brought into contact with each other in the process of measuring the surface of the sample 20, thus making the microlens 15 or the surface S of the sample 20 contaminated or scratched.
So as to prevent the optical system and the surface S of the sample 20 from being brought into contact with each other, accordingly, a separate stage is adopted to convey the optical system or the sample in a direction of an axis z, but in this case, a high degree of precision should be needed to control the optical system in the direction of the axis z. Furthermore, the formation of the separate stage makes the whole configuration of the system undesirably complicated.
In scanning the surface of the sample using the conventional confocal optical system, further, so as to locate a single beam spot or optical probe over the whole area to be measured on the surface of the sample, as shown in FIG. 4, an actuator should be used to finely move the nano stage on which the sample is mounted.
However, a long period of time is needed to move the single beam spot over the area to be measured, and further, the whole performance of the optical system is lowered due to the vibrations generated by the activation of the actuator.
So as to solve the above-mentioned problems, as shown in FIG. 5, an optical system having multiple optical probes is provided wherein a plurality of beam spots or optical probes are irradiated at the same time, so that the information corresponding to the number of beam spots is obtained by the unit of page through the photo detector.
Referring to FIG. 6 showing the optical system having multiple optical probes, in acquiring the surface information over the whole measuring area (that is, the area indicated by the dash-dot line of FIG. 6), advantageously, each beam spot is moved only within the area (macrocell, which means the area of x0 and y0 of FIG. 6) reduced in inverse proportion to the number of beam spots.
When compared with the existing single beam spot, the moving line of each beam spot is further shortened, but the optical system having multiple optical probes still needs a long period of time for moving the beam spots over a two-dimensional area in a longitudinal direction (in the direction of y) thereof and in a traverse direction (in the direction of x) thereof by given step. That is, if scanning within the multiple optical probe arrangement area (unit) being currently measured is finished, the multiple optical probes should be moved to the area adjacent to the scanned area and stop there, and after that, the beam spots should be moved in the longitudinal direction and in the traverse direction by given step. The processes are repeatedly carried out.
As the size of the measuring object becomes large, recently, it is hard to measure a large area with a high resolution limit, and according to the conventional optical system having the multiple optical probes, the movements of the beam spots for filling the surface of the sample and the movements and stop of the beam spots to the unit positions of the multiple optical probes are repeatedly conducted one by one to achieve the measurement of the surface of the sample, thus needing a substantially long period of time for measuring the large area and lowering the efficiency of quality inspection.